To provide comfort for truck drivers and reduce driving fatigue experienced by operators of truck vehicles, it is desirable to suspend the operator's cab by utilizing a vibration isolation and shock absorption device intermediate the truck chassis and cab which reduces the shock, vibration and consequent pounding the driver experiences during the operation of the vehicle. Additionally, the continued application of vibration and shock forces to the cab results in structural damage which ultimately results in increased maintenance costs.
The load carried by a truck vehicle is supported by the frame which is resiliently carried by suspension springs and supported by the truck wheels. Suspension springs have a high rate of stiffness which makes the ride more jarring on the operator of the vehicle. To dampen the vibration and shock transmitted to the cab, suspension systems have been employed utilizing conventional hydraulic automotive shock absorbers and air springs to reduce jounce and rebound movement of the cab with respect to the truck frame. Typically in the prior art, the air springs and shock absorbers were connected directly to the longitudinal side beam members of the truck frame such that the forces transmitted to the cab were at points remotely located from the cab center of gravity and consequently resulted in substantial rolling movements and cab sway. For example, in U.S. Pat. No. 3,944,017, issued Mar. 16, 1976, a suspension device for a truck cab is disclosed where air springs are used which have a relatively low spring rate to isolate the jounce and vibration of the truck frame from the cab. Shock absorbers are also utilized which contain internal jounce and rebound bumpers that limit the extent of vertical movement of the cab with respect to the truck frame. The air springs are shown to be oppositely mounted immediately above the truck frame and located in direct vertical alignment with the frame. The shock absorbers are also oppositely mounted but with central axis extending in an outward direction from the vertical axis of the frame member where the central axes of the shock absorbers are inclined to the displacement axes of the air springs. Thus, in U.S. Pat. No. 3,944,017, and similarly in the prior art, those forces transmitted to the cab by the air springs and shock absorbers are at a substantial distance from the center of gravity of the cab thereby causing increased shock, lateral sway and rolling. Consequently, the driver experiences greater discomfort and the cab itself sustains higher force load levels which ultimately results in structural failure.